BRACHIOPODA. 361 



nearly equal to the length of the hinge. On each lateral slope are from two 

 to four low radial undulations or plications, all of which are sharply defined at 

 the umbones. Surface covered with very fine, closely crowded concentric lines 

 ■which are granulous and were originally fimbriate. Length of typical speci- 

 men, 21 mm.; greatest width, 22 mm.; length of hinge, 10 mm. 

 Hamilton group. Centerfield and Canandaigua Lake, N. Y. 



Spirifer mucronatcs, Conrad, var. posterus, var. nov. 



PLATE XXilV, FIGS. 27-31 



A late variety of the typical Hamilton form, characterized by its small size, 

 usually narrow bodies and acuminate cardinal extremities. 

 Chemung group. Tompkins county, N. Y. 



Spirifer disjunctds, Sowerby, var. sdlcifer, var. nov. 



plate: XXX, FIG. 16. 



This variety is distinguished by the sharply defined median sulcus on the 

 folds of the brachial valve. It has heretofore been embraced within the limits 

 of S. disjundus, Ijut the character referred to appears to be persistent. 



Chemung group. Near Olean, N. Y. 



Spirifer Williamsi, sp. nov. 



PLATE XXXVII, FIGS. 20, 21, 22. 



Shells of the form of Spirifer increbescens. Hall, and varying but little in size. 

 Median fold and sinus well developed. The latter bearing usually three, some- 

 times four plications, finer than those on the lateral slopes. Of these the me- 

 dian plication is generally the strongest. This, however, is not always the 

 case, the arrangement of these plications being frequently quite irregular. The 

 median fold generally bears a median groove and one lateral plication on each 

 side. On each lateral slope of the shell are seven or eight plications. 



A normal example measures: Length, 15 mm. ; width on hinge, 24 mm. 



Chemung group. Allegany county, N. Y. 



